(Reuters) -The Slovak government halted purchases of COVID-19 vaccines on Wednesday pending a review of their safety by the Slovak Academy of Sciences, Prime Minister Robert Fico said.

Fico, a populist who has himself declined coronavirus vaccination, has long criticised the COVID policies of the previous governments, including vaccination campaigns before his return to power in 2023.

Fico told a televised briefing that based on a 2023 agreement signed by a previous administration, Slovakia was still due to receive 300,000 more vaccine doses for around 5.7 million euros ($6.48 million). He did not name the suppliers.

"We have an expert opinion from a registered expert that the vaccines used in Slovakia contained enormously high levels of DNA and substances which the producer did not show in the packaging material," Fico told a news conference.

"Therefore the decision to not take or pay temporarily (for the remaining vaccines) until we have more information is right," he said.

The cabinet's decision to pause vaccine purchases followed a recommendation by vaccine opponent Peter Kotlar, the government's envoy in charge of reviewing pandemic policies.

Kotlar has claimed, without evidence, that vaccines based on mRNA technology were not safe and called on the government to stop inoculations.

Producers of mRNA vaccines Moderna and Pfizer did not immediately respond to a request for comment.

Slovak drug regulator SUKL last month sharply criticised Kotlar's views, saying they were unscientific and dangerous, and said it was considering filing a criminal complaint for spreading panic.

The main Slovak opposition party, Progressive Slovakia, said Fico was using Kotlar's "conspiratory delusions" to distract attention from his government's policy failures.

Fico has repeatedly doubted the benefits of COVID-19 vaccinations, and organised a protest that went against lockdown rules during the pandemic.

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(Reporting by Jan Lopatka and Jason Hovet in PragueEditing by Bill Berkrot)